The present invention relates to a test mill forming a reduced-scale model of an industrial mill used in the mining industry and comprising a rotary shell supported by a frame and capable of rotating, at a variable speed, about its longitudinal and horizontal axis, said shell being capable of containing a certain amount of grinding media and of receiving a certain amount of material to be ground so as to be able to operate under conditions comparable with those of an industrial mill.
The invention is aimed more particularly at the field of wet milling, particularly as used in the mining industry to grind ores such as iron ore or copper ore for example. These mills contain a grinding charge compriseing of grinding media such as balls, cylpebs, boulpebs, bars, etc. and grinding occurs as the mill rotates under the effect of impact and friction occuring within the grinding charge. The material to be ground is converted into a wet pulp which comprises of the actual mineral, of sterile matter known as xe2x80x9cganguexe2x80x9d and of water.
The operation which follows grinding comprises in extracting the valuable mineral from the pulp, that is to say in separating the mineral from the gangue. This operation is performed in a flotation cell. This is a tank in which there is a stirrer to agitate the pulp and which calls upon surface-tension phenomena. Gases and chemical reagents are injected into the liquid medium to make the mineral spaces hydrophobic. The mineral with hydrophobic surfaces bind to the gas-liquid interface of the gas and air bubbles. These bubbles thus harvest the mineral by rising to the surface where they resemble a mineral-rich froth which is removed by overflowing.
The yield of a flotation cell, particularly the rate of recovery of the valuable mineral is directly influenced by the pulp chemistry and the state of particle surface which, in turn, depends on the mill operating conditions and on the nature of the grinding media. Furthermore, the chemical composition of the pulp may have a beneficial or detrimental effect on the consumption of reagents injected into the flotation cell.
It will therefore be appreciated that it is essential to be able to make regular and frequent survey of the pulp in order to assess the impact of the milling conditions on the pulp chemistry and make a reliable diagnosis of its operating conditions. Unfortunately, at the present time, this type of diagnostic and analysis cannot be performed in the plant and a laboratory investigation presents great difficulties as regards the producibility of the plant situation and as reliability of results e.g. the scale up to the plant of laboratory research results.
Indeed the only method used to date and described in an article published by the researchers of ENSG and CNRS, in International Journal of Mineral Processing, No. 28 (1990) pages 313-337 proposes that a pulp and a chemical environment equivalent to those of an industrial mill to be studied and monitored be recreated in the laboratory.
This method uses a mill in closed circuit with an independent investigation chamber. The pulp is recreated in the investigation chamber then injected into the mill to be ground. After the grinding operation, the pulp is transferred to a flotation cell.
It is clear that during grinding, the composition of the pulp and the atmosphere in the mill change. Now, the atmosphere is of great importance, particularly its oxygen content. In consequence, at the end of grinding, the chemical state of the pulp (and by chemical state we mean not only the composition of the pulp but also the chemical medium in which it moves) has changed and the conditions are no longer intended industrial conditions for carrying out the flotation test.
The object of the present invention is to provide a test mill which makes it possible to recreate the operating conditions of an industrial mill and to perform continuous and in-situ analysis and adjustment of the chemical state of the pulp during the grinding operation without it being necessary to prepare the pulp in advance in an independent chamber.
To achieve this objective, the present invention proposes a test mill of the kind described in the preamble, which is characterized in that the shell is divided, in the longitudinal direction, by a perforated transverse partition, into a grinding chamber and a measurement chamber, in that the perforations in the partition are sized to hold the grinding charge back and allow the ground material to pass through, and in that the shell comprises a series of injectors allowing fluid products to be injected into the grinding chamber.
The shell is preferably supported by a moving chassis to which the two bases are connected by means of a fixed bearing and a rotary joint.
The measurement chamber contains a series of measurement instruments supported by a bracket fixed to the fixed bearing.
The injectors are preferably arranged in several longitudinal rows supplied respectively by supply lines from a buffer chamber provided on the base opposite the measurement chamber and supplied axially with injection fluids through its support bearing.
The pulp formed during the grinding operation in the grinding chamber and which can flow freely through the transverse partition into the measurement chamber can be analysed at will using the measurement instruments during the grinding operation and without interruption thereof. Furthermore, the injectors of gas into the grinding chamber make it possible to adjust and control the chemical state of the pulp.
The mobility of the mill allows it to be moved around on an industrial site where it can operate in parallel with the industrial mill.
Other objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.